and a dimension table to easily convert city, state into their string versions and also provide other attributes (e.g. GPS coordinates).

My questions are:
1. I'm including 'total_calls' in the schema even thought it could easily be calculated from inbound + outbound. I did this for simplicity in a REST call, is that a bad idea?
2. I'm adding a 'null' row to show all the calls for a given month regardless of city or state, again to simplify the client side. It adds a row and is somewhat sparse but preferrable by the developer. Acceptable practice?